This invention relates to a procedure for quantifying a person's ability to track changes in size and in particular to a method and apparatus for testing eye-hand coordination in tracking a changing-size image in the presence of various visual perturbations.
Psychophysical evidence supports the idea that the human visual pathway computes an object's rate of change of angular size rather independently of the object's trajectory and rather independently of other visual parameters including contrast and intensity. This independence can provide a basis for accurately judging the component of an object's velocity along a line through the eye in the working visual environment where many visual parameters vary simultaneously, and data acquired using such a basis can be very useful in predicting a subject's performance in tasks of eye-limb coordination, especially where visual information is largely restricted to the changing-size channel.
A review of the state-of-the-art reveals that there has been reported evidence that the visual pathway processes motion-in-depth information in several channels that are, to a first approximation, independent of each other. These include channels sensitive to changing size and channels sensitive to the relative velocities of the retinal images.
The defining property of a channel is that it is sensitive to one feature of the stimulus while being comparatively insensitive to all other features of the stimulus. There is one clear advantage for an organism of processing a visual system that operates as though composed of channels: in the complex, everyday visual world a channel would respond to one particular stimulus feature, unperturbed by all other accompanying visual stimuli. Thus, channel operation might go some way to explaining the notable reliability of eye-limb coordination exhibited by skilled individuals such as airplane pilots.
There are several flying tasks in which the pilot must accurately control his distance from an object in the face both of continuous perturbations of position in three dimensions, and of continuous perturbations of light intensity. It is proposed that the changing-size channels might be involved in the performance of such tasks.
Suppose, for example, that a pilot's task is to maintain a constant distance from a second airplane. If he starts to move closer, parts of the second airplane (e.g., rivets, identification markings) will appear to grow progressively larger at a rate determined by the speed with which he is approaching the other airplane. It is proposed that the changing-size channel is directly sensitive to the rate of change of size and, furthermore, it has been demonstrated that the changing-size channel is comparatively insensitive to sideways motion and to flicker. Thus, the changing-size channel could provide the pilot with a basis for reliably detecting his approach to the other airplane, even when there is appreciable sideways motion relative to the other airplane, and even when light intensity is fluctuating due, for example, to changes in his attitude relative to the sun. By reliably signalling "slowly approaching", and "slowly moving away" the changing-size channel could aid the pilot to successfully "hunt" around the desired distance from the other airplane.
In the past conventional psychophysical methods have been used to measure visual sensitivity to changing-size and to investigate the dynamic properties of the changing-size channel. However, it is not necessarily true that conventional psychophysical measurements of detection sensitivity will reliably predict an individual's performance of a task that demands skilled eye-limb coordination. For example, even if it is the case that the changing-size channel is important in formation flying, previous psychophysical measurements of changing-size sensitivity need not necessarily predict the accuracy with which a pilot can maintain distance from a second airplane, since the previous psychophysical measurements were restricted to simple visual detection sensitivity, threshold elevation and aftereffect strength: thus, in previous experiments, it was not required that subjects use changing-size information to perform a demanding task of eye-limb coordination.
In accordance with the foregoing it is seen that there currently exists the need for procedures and devices adapted to measure the precision with which a subject tracks a changing-size stimulus, and in particular to assess the subject's eye-hand coordination when the stimulus is processed by his changing-size channel alone. Furthermore, when flying an airplane or helicopter the pilot's changing-size channel must operate reliably even when the changing-size stimulus is accompanied by fluctuations of brightness and varying sideways motion. Therefore, it is also desirable that in the testing procedures the changing-size tracking stimulus can be accompanied by correlated or uncorrelated flicker and/or sideways motion. The present invention is directed toward providing a method and apparatus that will accomplish these ends.